The invention described herein relates to an airborne gas storage system and method, and more specifically to a system and method for storing a greater amount of a pressurized gas on board a launch vehicle, and providing access to a greater portion of said gas.
Various launch vehicles, such as rocket powered vehicles, will at times have a need for a source of pressurized gas. For example, liquid propellant rocket engines typically have one or more tanks on board which store propellant for the rocket engine. Propellant tanks such as those which store liquid oxygen (LOX) or kerosene, typically require tank pressurization in order to expel propellant at a controlled rate to the rocket engines or to maintain tank structural integrity. Certain gases are typically employed for this application because they do not condense at propellant temperatures. A gas which is regularly employed for this purpose is helium.
In a typical use of helium for this purpose, prior to lift off of a launch vehicle which employs liquid propellant, ground support equipment (GSE) will load pressurized gaseous helium (GHE) into flight storage bottles at ambient temperatures. The pressure at which the GHE is stored in the flight bottle provides for the flow of GHE from the flight bottle to the propellant tanks. In a typical application, many containers may be necessarily employed to provide the desired amount of helium gas.
The inventors have recognized that it would be desirable to employ a pressurized gas supply system which is configured to hold a large amount of pressurized gas and then provide access to substantially all of the gas so as to reduce the amount of residual gas remaining in the bottle. The inventors have further recognized that such a system is desirable if it is configured to use systems and components already present on the particular airborne craft, and significant modifications do not have to be made to the current system in order to employ the system described herein.
Described herein is a system and method for providing a source of pressurized gas. The system may include a bottle which is configured with sufficient structural integrity to receive and hold a stored gas where the bottle includes at least one valve device for controlling the inflow and outflow of the stored gas. Locatable within the bottle is at least one heating device configured so as to provide heat transfer from the device to the gas contained within the bottle so as to affect the gas pressure. The system may further include a supply line connectable to the first valve device which provides for directing the flow of the gas to a remote location.
In one configuration of the invention, the system described herein may be locatable aboard a rocket powered launch vehicle which employs a source of pressurized gas for purposes of pressurizing a propellant tank. For example, in liquid fuel rockets, an inert gas such as helium may be employed to pressurize the propellant tanks to provide constant propellant flow and to maintain tank structural integrity during flight. The system described herein is configured to control the pressure of the helium within the storage bottle and provide for the flow of the pressurized helium gas to the propellant tanks.
When helium or other inert gases are stored, the bottle may be configured to receive and store the gas in an extremely cold, high density, supercritical state. The supercritical helium is storable in the bottle at a high pressure. In one configuration of the invention, the heating device performs the task of heating the supercritical helium in the bottle to provide a desired pressure within the bottle. Pressurized gas may then exit the bottle and be directed to a remote source such as a propellant tank.
In yet another configuration of the invention, the heating device may comprise a heat exchanger through which a medium may pass which transfers its heat to the contents of the bottle. One medium may be the helium gas itself which is routed from the bottle to a remote heat exchanger, heated, and then returned to a heat exchanger in the bottle. The remote heat exchanger may employ hot gas from the propulsion system of the launch vehicle as a heat source. Other self-contained heaters, such as an electric heater, may also be employed for this purpose.
When the heated helium gas is passed through the heat exchanger in the bottle it transfers heat to the contents of the bottle. This transfer of heat from the medium to the stored content has the advantage that the medium is now cooled to the point that it is not hot enough to damage down stream components in the system. The medium exiting the bottle heat exchanger may then be routed through an external supply line to its ultimate destination, which may be a propellant tank.
In the configuration of the invention where the system is configured to store and provide access to a high density, supercritical gas such as helium, the bottle apparatus employed for this purpose may include an inner container portion (pressure vessel) which is constructed of a material of sufficient strength and ductility to provide for the storage of the gas at extremely low temperatures. In yet another configuration of the invention, the pressure vessel portion may be constructed of annealed Extra Low Interstitials (ELI) grade TI-6Al-4V (titanium alloy), because this singular grade has a very low specific heat and thermal conductivity, very high strength, adequate ductility and low density. The bottle may be further configured with at least one valve device for controlling the flow of helium gas in and out of the bottle.
Disposed around the pressure vessel portion may be at least one temperature control layer. This temperature control layer may be composed of multiple elements but whose principle purpose is to reduce the flow of heat from the external environment to the contents of the pressure vessel and to remove heat from the pressure vessel itself. In one configuration the pressure vessel is surrounded by a shroud which creates an annulus through which coolant flows. Liquid helium may be used as the coolant to cool and maintain the pressure vessel and the contents of the pressure vessel within the desired temperature band by intercepting heat coming from the environment and removing heat from the pressure vessel itself. The external surface of the shroud may be covered with a foam or ceramic fiber batting insulation material to minimize the amount of coolant required.
In yet another configuration the temperature control layer is composed of a vapor cooled shield. The vapor cooled shield is formed by placing a layer of insulation in direct contact with the pressure vessel exterior wall, next layering a thermally conductive metallic foil, and finally placing tubing which contains coolant in contact with the metallic foil layer. The coolant may be supplied from the contents of the pressure vessel or from an independent source and the flow controlled by one or more valves. These layers are then covered by insulative foam or ceramic batting. In this configuration, the pressure vessel is cooled by its contents boiling off, where boiled off gasses leave the tank through an orifice.
As was described above, the bottle may enclose a heating device for heating the contents of the bottle and thus controlling the internal temperature and pressure. In yet another configuration of the invention, the bottle heat exchanger may comprise an inlet manifold configured to receive the heated medium from the remotely located heat exchanger. Extending from the inlet manifold may be at least one tubular shaped member extending substantially through the inner volume of the container element. In connection with the tubular member may be a turnaround manifold which is further connected to another tubular member which extends through the inner volume of the container element in a direction substantially opposite to the first tubular member. This tubular member is further in connection with an exit manifold which provides for directing the pressurized gas which has been substantially cooled by fluid within the pressure vessel, to a supply line outside the container element.
In yet another configuration of the invention, the pressure vessel is configured with a polar aperture configured so as to enable the installation and removal of the heat exchanger. The aperture may be further sized so as to enable the welding of the pressure vessel subcomponent from the inside of the container so as to provide for a high quality weld with minimal defects. The aperture may further provide for the insertion of inspection tools, radiographic film and other devices which facilitate the inspection of any weld performed in the manufacture of the pressure vessel. In yet another configuration of the invention, the bottle is supported at the base by a flex support plate which provides a tailored flexibility and is high temperature resistant. The flex plate can provide an interface for the influx of coolant to the temperature control layer and also provide a gas tight seal to the element of the temperature control layer. The flex plate further provides a tortuous path for heat to flow from the environment to the inter container, and also provide passages for cooling to substantially remove the heat that does leak in before it reaches the pressure vessel. The flex plate may be fabricated from aged Inconel 718 which has high strength, high modulus and relatively low thermal conductivity as well as machinability and weldability.
In operation, the bottle assembly described above is first positioned aboard the launch vehicle or within the environment in which it is to operate. Depending on the type of gas employed and the condition in which it will be pumped into the bottle, certain preparations are made for the bottle to receive the gas. Once the desired amount of gas is pumped into the bottle and the bottle temperature and contents temperature and pressure are at desired levels, a valve device employable for controlling the outflow of gas may be manipulated to control the amount of pressurized gas which exits.
As the bottle empties, a heating device locatable within the bottle may be activated and employed so as to transfer a desired amount of heat to the remaining gas in the bottle. This transfer of heat has the effect that the bottle pressure is increased relative to a bottle without such a heat transfer thus providing a continuous supply of gas within a desired pressure range over a greater period of time. This heat also provides for the ability to use all or substantially all of the gas loaded in the tank. The amount of heat transferred to the bottle contents is controlled to adjust the exit temperature from the bottle heat exchanger so as to maximize the total amount of energy transferred to the propellant tanks so as to minimize the total amount of helium required without causing overheating of the downstream components or propellant tank. The design of the heat exchanger maximizes the free convection between the heat exchanger and the bottle contents so as to minimize the total heat transfer area required. External acceleration caused by the flight of the rocket vehicle also serves to enhance the heat transfer since the acceleration positively affects convection within the bottle. In the configuration of the invention where the stored gas is high density, supercritical helium, the gas may be initially stored at a temperature of approximately 20 degrees R and approximately 4600 PSI. If a self-contained heater positioned within the tank is employed, this heater along with the valve which controls the outflow gas are manipulated to provide a pressurized gas at a controlled rate.
In the configuration of the invention where an external heat exchanger is employed, the bottle contents (cold helium) is first routed via a supply line to the external heat exchanger where it picks up heat rejected from the rocket engine or some other source. The now hot helium may then be passed through the heat exchanger contained within the bottle where it gives up some of the heat acquired in the external heat exchanger to the gas in the bottle and then exits in a condition still hot enough to effectively pressurize a tank such as those employed as propellant tanks aboard launch vehicles employing rocket motors.
Prior to employing the bottle assembly for providing a source of pressurized gas, a particular procedure for loading the gas may need to be followed, especially in the case where supercritical helium is the stored gas. In the situation where the pressurized gas is employed to pressurize a propellant tank, prior to launch of the vehicle, the bottle assembly may be connected to ground support equipment. Initial chilldown of the bottle assembly is accomplished by flowing LHe coolant through the GSE, pressure vessel and temperature control layer and out through vents. Coolant flow is continued until the pressure vessel is substantially at liquid helium temperature and is substantially full with liquid helium. Flow through the pressure vessel and temperature control layer may be independently controlled using the GSE. Once the bottle and system are chilled and the bottle is substantially filled with LHE the pressure within the pressure vessel is raised using a liquid helium pump in the GSE until the desired operating pressure is achieved. Coolant flow through the temperature control layer continues at a low pressure throughout this process to continue to remove heat flowing towards the pressure vessel from the environment and also to remove the heat of compression from the fluid within the pressure vessel. Coolant flow may be adjusted to achieve the desired temperature and pressure conditions within the bottle with a minimum amount of coolant.